Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 182,956	$ 366,122	$ 350,994
AFS investment securities
Net unrealized gains (losses)	41,145	(250,273)	(63,714)
Unrealized (losses) on AFS securities transferred to HTM securities	0	(67,604)	0
Amortization of net unrealized losses on AFS securities transferred to HTM securities	9,025	9,870	1,551
Reclassification adjustment for net losses realized in net income	64,940	1,922	16
Income tax (expense) benefit	(30,560)	78,159	15,557
Other comprehensive income (loss) on AFS investment securities	84,550	(227,926)	(46,591)
Fair value adjustment on cash flow hedges	(13,254)	3,626	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	13,930	(212)	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	(956)	(54)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(280)	3,360	0
Defined benefit pension and postretirement obligations
Amortization of prior service cost	(326)	(325)	(148)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	0	1,494
Net actuarial gain (loss)	24,091	(51,745)	25,519
Amortization of actuarial loss (gain)	(29)	658	4,594
Income tax (expense) benefit	(6,304)	13,495	(7,803)
Other comprehensive income (loss) on defined benefit pension and postretirement obligations	17,432	(37,917)	23,656
Other Comprehensive Income (Loss), Net of Tax	101,703	(262,483)	(22,935)
Comprehensive income	$ 284,659	$ 103,639	$ 328,059